Here's another stock market measure that looks like the tech bubble era

A key stock market valuation metric has risen to a level it's only ever been at once before in recent history — and that was during the giant tech bubble of 2000.

S&P Global Market Intelligence provided data which show that the current price-earnings ratio on trailing GAAP earnings per share is at 25.3 times, second only to the trailing P/E which peaked at 31.7 times during the overheated bull market of 2000. S&P studied P/E data from bull markets going back to World War II.

"It concerns me that the P/E is high," said Sam Stovall, chief equity strategist at S&P Global Market Intelligence. Stovall said high P/Es make the market vulnerable to any unexpected shocks.

"People have been saying the sky is falling for so long that nobody is paying attention any longer," he said. But Stovall said that does not mean the bull market is about to end.

The current trailing P/E, as of Aug. 15, was more than 600 basis points above the average bull market P/E of 19.2 times. Elevated P/Es can make investors nervous, but S&P says they are not good market-timing tools. In fact, 7 of the past 12 bull markets topped out below the long-term average bull market P/E.

The S&P strategists studied sectors with below-average P/Es for opportunities, and found 10 stocks they believe have attractive valuations. They looked at S&P Composite 1500 subindustries with below-average P/Es, favorable ratings and rolling 12-month relative strength.